The present invention relates to a semiconductor device, and more specifically to a semiconductor device such as a semiconductor memory circuit device employing semiconductor non-volatile memory elements which enable information to be written down and erased, as well as to a method of manufacturing the same.
Conventionally known semiconductor non-volatile memory elements can be represented by insulated gate field effect transistors of the type which employs a trap in the gate insulation film or of the type which employs a floating gate. With the insulated gate field effect transistors of this type, a threshold voltage changes from one stable value to another stable value when the electric charge is poured into the trap or the floating gate in the gate insulation film due to hot carriers which are produced by the tunnel effect or the avalanche breakdown. The state of the one threshold voltage is corresponded to, for example, "0" in the binary signal and the state of the another threshold voltage is corresponded to "1" in the binary signal.
The above-mentioned electric charge can be removed by a suitable method.
Therefore, the insulated gate field effect transistors of the above-mentioned type have the advantage that they can be used as non-volatile memory elements which enable information to be written down and erased.
A plurality of the semiconductor non-volatile memory elements are orderly arrayed, for example, on a semiconductor substrate, and are selected to read or write information.
To write the information, the above-mentioned semiconductor non-volatile memory elements require signals of a voltage which is greater by several times than the voltage of the signals which are used for reading the stored information.
However, since limitation is often imposed on the signal levels depending upon the characteristics of the circuit elements, the semiconductor memory circuit device requires a specially designed circuit to deal with the signals of the high levels.
Further, the construction of the semiconductor memory circuit device tends to be complicated depending upon the circuit device for processing the signals of high levels. Therefore, particular attention must be given with regard to that the semiconductor substrate will not become bulky and performance such as operation speed will not be decreased.
Further, the semiconductor circuit device must be realized based chiefly upon the insulated gate field effect transistors, and it is further required to employ bipolar transistors to constitute the circuit as well as to enhance the function. It is therefore required to realize the semiconductor circuit device in the form of a so-called semiconductor integrated circuit which is formed on a piece of a semiconductor substrate. In producing the semiconductor integrated circuit devices, furthermore, it is required to enhance the manufacturing efficiency. Consequently, it is required to realize the electronic circuits through a manufacturing process which is simplified as far as possible.